Use of the unused duration injection units in an array to reduce oscillations during impedance injection for corrections of problems

ABSTRACT

A control module controls impedance injection units (IIUs) to form multiple connection configurations in sequence. Each connection configuration has one IIU, or multiple IIUs in series, parallel or combination of series and parallel. The connection configurations of IIUs are coupled to a high-voltage transmission line. The control module and the IIUs generate rectangular impedance injection waveforms. When the waveforms are combined and injected to the high-voltage transmission line, this produces a pseudo-sinusoidal waveform.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/893,673 filed Jun. 5, 2020, which claims benefit of priority fromU.S. Provisional Application No. 62/939,413 filed Nov. 22, 2019, thedisclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to using available resources oftransformerless flexible alternating current transmission system(TL-FACTS) based impedance injection units to manage disturbances on ahigh voltage (HV) transmission line.

BACKGROUND

The current move in the industry is to use modular transformerlessflexible alternating current system (TL-FACTS) based impedance injectionunits (IIUs) for distributed and localized line balancing and localizedcontrol of disturbances in the high voltage (HV) transmission lines 108of the grid, as shown in FIG. 1 . This local control is in addition toutility-based control of power flow over the HV transmission lines. Thelocal control of the HV transmission lines is achieved by use ofintelligent impedance injection modules (IIMS) 300 connected in serieswith the transmission lines and comprise a number of IIUs typicallyconnected in a series-parallel configuration. The parallel connectedIIUs switched in synchronized fashion are used to provide increasedcurrent carrying capacity for the transmission lines while the seriesconnected IIUs can be used to increase the injected impedance voltage ina cumulative fashion. The IIMs 300 are coupled to the HV transmissionline 108, typically in a distributed fashion as shown in FIG. 1 toenable the local control. Since the IIMs 300 are connected in serieswith the HV transmission line 108, their injected impedance voltages arealso cumulative over the HV transmission line 108. There is a need inthe art for ongoing improvements.

SUMMARY

A method of operating impedance injection units (IIUs), an impedanceinjection unit system, and a computer-readable media are described invarious embodiments.

One embodiment is a method of operating impedance injection units. Themethod includes controlling, by a control module, a plurality of IIUs toform multiple connection configurations in sequence. Each connectionconfiguration includes one IIU, or multiple IIUs in series, parallel orcombination thereof. Each connection configuration is coupled to a highvoltage transmission line. The method includes generating a plurality ofrectangular impedance injection waveforms. The generating is by thecontrol module through the multiple connection configurations of IIUs insequence. When the rectangular impedance injection waveforms arecombined and injected to the high voltage transmission line, thisproduces a pseudo-sinusoidal waveform.

One embodiment is an impedance injection unit system. The system has aplurality of IIUs and a control module. The control module is to directthe plurality of IIUs to form connection configurations in sequence.Each connection configuration has one IIU or multiple IIUs in series,parallel or combination thereof, coupled to a high-voltage transmissionline. The control module is to generate, through the connectionconfigurations of IIUs in the sequence, rectangular impedance injectionwaveforms. The rectangular impedance injection waveforms are to combineand inject to the high voltage transmission line, to produce apseudo-sinusoidal waveform on the high-voltage transmission line.

One embodiment is instructions on a tangible, non-transitory computerreadable media. When the instructions are executed by a processor, thiscauses the processor to perform various actions. The processor is todirect a plurality of IIUs to form connection configurations insequence, when the IIUs are coupled to a high-voltage transmission line.Each connection configuration includes one IIU or multiple IIUs inseries, parallel or combination thereof. The processor is to generate,through the connection configurations of IIUs in the sequence,rectangular impedance injection waveforms. The rectangular impedanceinjection waveforms are to combine and inject to the high voltagetransmission line, to produce a pseudo-sinusoidal waveform on thehigh-voltage transmission line.

Other aspects and advantages of the embodiments will become apparentfrom the following detailed description taken in conjunction with theaccompanying drawings which illustrate, by way of example, theprinciples of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure are illustrated by way of example and notlimitation in the figures of the accompanying drawings in which likereferences indicate similar elements.

FIG. 1 is a diagram illustrating a conventional power grid system with adistributed and hierarchical intelligent control system. (prior art)

FIG. 2 is a block diagram illustrating a conventional dynamicintelligent impedance injection module with local and global timesynchronization capability. (prior art)

FIG. 3A is a circuit diagram illustrating a local master control moduleof a TL-FACTS based IIU having an associated local clock according toone embodiment.

FIG. 3B is a circuit diagram illustrating a local master control moduleof a TL-FACTS based IIU having an associated local clock that can besynchronized to a global clock according to one embodiment.

FIG. 4 is a circuit diagram illustrating an example of atransformer-less flexible alternating current (AC) transmission system(TL-FACTS) based impedance injection unit (IIU), where one or more IIUsmay constitute an impedance injection module IIM 300.

FIG. 5 is an example block diagram illustrating an IIM having a 2×2series-parallel connection comprising four TL-FACTS based ITUs accordingto one embodiment.

FIG. 6 is an example illustrative diagram of the IIM having two sets ofparallel connected TL-FACTS based IIUs interconnected in series. A 2×2Matrix of FIG. 5 providing two rectangular waveforms from the two setsof series connected IIUs 400 in a synchronized fashion that whencombined, generate a pseudo-sinusoidal wave for injection on to the HVtransmission line.

FIG. 6A shows the synchronously-generated and injected rectangular wavesfrom each of the two series connected groups of two parallel connectedITUs of the IIM 300 of FIG. 5 .

FIG. 7 shows an 8 IIUs configured in four parallel groups, each grouphaving two IIUs in parallel and the four groups connected in series toform an IIM.

FIG. 7A shows the injected output from the four groups of dual IIUs ofFIG. 7 with their injection start and end times adjusted in asynchronized fashion to generate a pseudo-sinusoidal waveform thatsmooths to a sinusoidal waveform 701 when injected on the HVtransmission line.

FIG. 8 shows the synchronously injected waveforms from each of the fourIIUs of the IIM that enable the modified injected waveform of FIG. 7 .

FIG. 8A is an example illustrative diagram 800 of the use of theun-utilized capability of the IIUs of the IIM in FIG. 7 . Diagram 800shows injecting additional rectangular waveforms to modify the pseudo-sinusoidal waveform 701 of FIG. 7A. This injection results in a modifiedwaveform which is smoothed to waveform 801. The smoothed waveformaddresses managing unexpected problems on the HV transmission line.

NUMBERING AND LETTERS IN FIGURES 100- an example grid 300- Impedanceinjection module (IIM) 108- High voltage (HV) 301-Sensor and powersupply transmission line 201- HV transmission 302-Local Intelligencecenters towers (LINC)s 203-Generators 303-High-speed communication link204- Substations 304- Power supply & sensing Transformer 205- Connectedloads 305- Communication link 206- System utility 400 A-v or B-v -squarewave injection from IIU 400A or 400B 207- Communication link 401-Impedance injection unit 408B-IGBT Switch 402- MasterControl--Intelligent with clock 409- DC Capacitor 403- Intelligentcontroller 410- Highspeed wireless 404A - Clock, synched to localcommunication clock 500 - Generation of sinusoidal 404B- Clock, synchedto global impedance injection clock 501 & 701- Smoothed injected 405-FACTS switch waveform 800- modifying the injected 406A & B- Injectionterminals waveform 801-x-nv nth additional 407- GPS satellite njectionfrom IIU at free time. 801- Modified impedance waveform 408A-IGBT switchcontrol 400A & B series connected dual 400A-v to 400B-v & injectionparallel switches 400-A1 & from the series groups A2 and 400-B1 & B2700-1 to 4 group of four dual 700-1v to 700-4v injected parallelconnected switched cumulative impedance voltages. connected in series t1to t4 -start times of the t1′ to t4′ - end times synchronized generatedof the synchronized generated impedance waveforms impedance waveforms d1to d4-duration of the s - the duration of short synchronized generatedpulse waveform generated impedance waveforms during unused period

DETAILED DESCRIPTION

Intelligent impedance injection modules (IIMs) comprising connectedtransformer-less FACTS (TL-FACTS) devices are used as impedanceinjection units (IIUs) for control of high-voltage (HV) transmissionlines. The IIUs generate and inject rectangular impedance waveformswhich if cumulatively large when injected create high-frequencyoscillations that interfere with control systems on the HV transmissionlines and user premises. By staggering and synchronizing the timing ofthe injection from the series connected IIUs or IIU groups, the injectedwaveform is converted to a pseudo-sinusoidal waveform to reducegeneration of oscillations. This method of injection leaves some IIUs orgroups of IIUs with very low utilization. The idle time of the IIUs areused to generate and inject impedance on to the HV power line and modifythe injected waveform to overcome unexpected disturbances when needarises.

Definitions

1. LOCAL: belonging or relating to a particular area or neighborhood,typically exclusively so. In this case the term local is used to denotea segment of the HV transmission typically line under a single localcontrol.

2. IMPEDANCE: is the measure of the opposition that a circuit presentsto a current when a voltage is applied. The term complex impedance maybe used interchangeably. Impedance extends the concept of resistance toAC circuits, and possesses both magnitude and phase, Impedance can beinductive, capacitive, resistive.

FIG. 1 shows the example system 100 that includes distributed impedanceinjection modules (IIMs) 300 distributed over HV transmission lines 108between substations 204. The IIMs 300 are directly attached to the HVtransmission lines 108 of the power grid and are suspended insulatedfrom ground on HV transmission lines suspended from HV towers 201.Generators 203 and loads 205 are typically connected to the HVtransmission lines 108 of the power grid at the substations 204. Thegroups of local IIMs 300 are communicatively connected or coupled to alocal intelligence center (LINC) 302 via high-speed communication links303 that allow for communication and response by the IIMs 300 in thelocal area at sub-synchronous speeds when required. The plurality ofLINCs 302 are also connected by high-speed communication links 303 toother neighboring LINCs 302 for coordination of activity of the localIIMs 300 groups. A supervisory utility 206 oversees the activity of thesystem 200A using command and communication links 207 connecting to theLINCs 302 and substations 204. The supervisory utility 206A is able tohave interactive control of the local IIMs 300 via the communicationlinks connecting it to the LINCs 302. The supervisory utility hassuperseding control of the LINCs 302 and the IIMs 300 at any time.

FIG. 2 is a block diagram showing the main components of an intelligentIIM 300. Referring to FIG. 2 , IIM 300 includes at least an impedancegeneration and injection module 401, an intelligent control capability402 with at least a clock with time synchronization capability, and ahigh-speed communication link 410.

FIG. 3A shows use of a local clock 404A coupled to an intelligentcontrol module 403 within each IIM to synchronize the generation andinjection of impedance on to the power line 108. The FIG. 3B shows useof a global clock 404B controlled typically by the GPS 407, coupled toan intelligent control module 403 to synchronize the generation andinjection of impedance on to the power line 108. The IIM 300 uses powerextracted from the HV transmission line 108 using a power transformer301A coupled to a sensor and power supply module 301 to provide thepower to the circuits of the IIM 300 including the intelligent controlunit 403, communication unit 410 and the IIUs 400.

FIG. 4 shows an example circuit diagram of a transformer-less flexiblealternating current transmission system (TL-FACTS) based impedanceinjection unit (IIU) 400 connected in series on the HV transmissionline. The IIU 400 is capable of generating inductive or capacitiveimpedance to be injected on to the power line 108. The IIU 400 comprisetwo leads 406A and 406B that are connected in series with the HVTransmission line 108. Four insulated-gate bipolar transistor (IGBT)switches 408B are used to connect the input line, lead 406A to theoutput line, lead 406B. The switching of the four IGBT switches 408B arecontrolled by switch controls 408A-1 to 408A-4 that are coupled to amaster control 402. The master control, for example intelligent controlcapability 402 of FIG. 2 , is coupled to a sensor and power supplymodule 301, which extracts power from the HV transmission line 108 forthe operation of the ITU 400 via the transformer 304. A DC capacitordevelops a DC voltage across itself that is used as injected impedanceinto the HV power line 108. Depending on the sequence of switching ofthe IGBT switches 408B an inductive or capacitive impedance can begenerated and injected on to the HV transmission line 108. Typically, anIIM 300 comprise a number of IIUs 400 that are connected in aseries-parallel configuration.

FIG. 5 shows an IIM 300 having a 2×2 configuration of IIUs 400. The IGBTswitches of the IIUs are enabled to switch to generate rectangularimpedance waveforms which get injected on to the HV transmission line.IGBT switches 408B have to be de-rated during application for theircurrent carrying capacity to improve reliability, in some embodiments.IGBT paralleling within IIUs 400 and multiple IIU paralleling withswitch synchronization in each IIM 300 are used to ensure adequatecurrent capability through the IIMs 300 connected in series with theline. The paralleled groups of IIU 400 may be connected in series withineach IIM 300 to increase the generated and injected impedance voltagefrom the IIM 300. The result of such a connection configuration is toincrease both the current carrying capacity and the generated injectedimpedance voltage from the IIM 300.

The injected waveforms from the series connected IIUs 400 groups, 400Aand 400B are additive and make up a rectangular impedance injectionwaveform of typically double the amplitude if the start and stop timesare synchronized. Such a large amplitude rectangular injection on to theHV transmission line 108 may result in oscillations being initiated andharmonics being injected on the HV transmission line 108. It will beideal if such oscillations and harmonic injections are avoided on the HVtransmission lines of the grid for improved stability and reliability ofoperation of the power grid. This can be accomplished by staggering theimpedance injection from various series connected IIUs 400 or groups ofparallel connected IIUs 400 where the groups are connected in series.

In some cases, individual capability of a single IIM 300 is insufficientto provide the impedance injection required. The resources from multipledistributed IIMs 300 s which are connected in series on the HV powergrid may be utilized to generate the total impedance injection needed.Staggering of start and stop times (or duration of injection) is neededin these cases to limit oscillations and injection of harmonics on theHV transmission line. Use of the synchronizable clock across IIMs 300enables such staggering of injected waveforms within an IIM 300 and/orbetween IIMs 300 by modifying the start and end times of the seriesconnected IIU 400 groups, the IIU 400 groups being IIUs 400 s connectedin parallel and switched simultaneously as previously discussed.

In certain instances, the HV transmission lines can experience suddendisturbances which may be local in nature. It will be ideal ifresponsive action can be initiated in the sensed local region to remedysuch disturbances and limit their spread.

It is optimum if the generated waveforms from the IIUs 400 of the IIM300 can be adjusted to represent a pseudo-sinusoidal impedance waveformwhen cumulatively injected on to the HV transmission line 108. IIM 300may comprise one or more IIUs 400 that are connected in series, parallelor series-parallel connections. A set of start-time-synchronized andduration-adjusted waveforms generated by four IIUs 400s connected in a2×2 array of FIG. 5 is shown in FIG. 6 . The 2×2-connected array of IIUs400 of the example IIM 300 comprise four IIUs, the first two IIUs 400-A1and 400-A2 forming a parallel-connected group 400A and the second twoIIUs 400-B1 and 400-B2 forming a second parallel-connected group 400-B.The waveforms generated by each of the parallel connected IIUs of agroup are synchronized to start, end and have same amplitude. The twoparallel connected groups 400A and 400B are connected in series to formthe example implementation of the IIM 300 of FIG. 5 . The IIM 300 ofFIG. 5 is able to generate impedance injection waveforms 400A-v and400B-v as shown in Fig.6A, the waveform 400A-v having a start at time t1and an end time t1′ with a duration d1, and the waveform 400B-v having astart time at t2 and an end time t2′ wherein the duration is d2 which isless than d1. The two waveforms are cumulative when injected onto the HVtransmission line as the two parallel connected IIU groups 400A and 400Bare in series and typically will smooth out to the sinusoidal waveform501 shown in FIG. 6 .

FIG. 7 shows another example IIM 300-2X comprising a 4×2 combination,four groups of two IIUs 400 in parallel, the four groups are connectedin series to form an IIM 300-2X. That is, each of the four groups 700-1to 700-4 are formed by paralleling two IIUs 400. Group 700-1 comprisingIIUs 400-A1 and A2, group 700-2 comprising IIU 400-301B1 and B2, 700-3comprising IIUs 400-C1 and C2, the group 700-4 comprising IIU 400-D1 andD2. The four parallel-connected groups of IIUs 700-1 to 700-4 areconnected in series to generate impedances 700-1 v to 700-4 v to beinjected on to the HV transmission line 108. The individually injectedimpedances 700-1 v to 700-4 v have start times staggered as t1, t2, t3and t4 with end times staggered as t1′, t2′, t3′ and t4′ providinginjection durations d1, d2, d3 and d4 respectively, as shown in FIG. 7A.These impedances, when injected onto the HV transmission line,cumulatively combine to provide a pseudo-sinusoidal waveform which getssmoothed to the sinusoidal waveform 701 due to the impedance of the lineas shown in FIG. 7A.

Considering FIGS. 7 and 7A, it is clear that the impedance generationcapabilities of all the groups of IIUs 700-1 to 700-4 of the IIM 300-2Xare not fully used in generating the impedance for injection on to theHV transmission line. In one embodiment, it is assumed that all of theIIUs groups 700-1 to 700-4 of the IIM 300-2X have equal capabilities forgeneration of impedance waveforms, as shown in FIG. 7A. The IIU group700-1 injects the rectangular waveform 700-1 v having a start time t1, aduration d1, and an end time at t1′. Furthermore, IIU 700-2 isconstrained to inject a waveform 700-2 v starting at a later time t2having a duration d2 that ends at t2′ before the 700-1 v tl' ends.Similar conditions are repeated for IIU group 700-3 and IIU group 700-4,resulting in each of the IIU groups that start later ends earlier withsmaller and smaller duration. Hence the later starting groups of IIUshave larger and larger unused capacity as clearly shown in FIG. 7A.

A sudden disturbance or a local disturbance that happens on the HVtransmission line can require an injection of inductive or capacitiveimpedances as corrective action. This corrective action can beaccomplished within the same injection cycle by generating shortduration pulses by the IIU groups 700 with their available unutilizedtime. The sudden or local disturbance is sensed by the sensors coupledto the IIM 300-2X or alternately sensors distributed over the HVtransmission line. The IIM 300-2X of the local area receives the senseddata, and using the intelligence built into it, develops an impedanceinjection response to the disturbance by taking into account theavailable resources including the unused capacity of the groups of IIUs700 of the IIM 300-2X.

The response defines the generation and injection of additional shortduration pulses of duration ‘s’, shown in FIG. 8 , during the unutilizedIIU groups' 700 available time. The additional short duration pulses aresynchronized with the normally injected impedance pulses using the localor global clock used by the IIM 300-2X generating the short pulses.These short-duration pulses are used to amend or modify the normallyinjected impedance injection waveform 701 to the example modifiedwaveform 801 to address the sudden or local disturbance identified onthe HV transmission line.

FIGS. 8 and 8A show the example short-pulse generation and injection ofthese short-duration pulses during the unused times of the groups of IIU700. FIG. 8 shows the short-duration pulse 801-3-1 v having a start timesynchronized to t1 and duration ‘s’ generated and injected by IIU group700-3 and also the additional short pulses 801-4-1 v having a start timeat t2 and duration ‘s’ and 801-4-2 v having a start time t3 and duration‘s’ being generated by IIU group 700-4 which when cumulatively injectedwith the regular injected waveforms 700-1 v to 700-4 v modify theoriginal injected and smoothed impedance waveform 701 to a modifiedsmoothed waveform 801 to be injected on to the HV transmission line 108to overcome the sudden or local disturbance that was sensed on the HVtransmission line 108.

As discussed previously, the additional pulses generated and injectedcan be either inductive or capacitive depending on the disturbancesensed and the response identified by the TIM 300-2X. Though the shortpulses are shown as having a fixed duration, it is not necessary to haveit so. The short pulses can have any duration without encroaching on theexisting impedance injection waveform from the group of IIUs 400.Similarly, the amplitude of the short pulses and the injected impedancewaveform are shown as being equal in magnitude from each of the groupsof IIUs. The equal magnitude injection is not always necessary oroptimum. The amplitudes of injected waveform can be different fromdifferent switch groups and the amplitudes and timing can be optimizedto respond to any line balancing, flow control or disturbance correctionneeds within the injection capability of the group of IIUs.

Even though the invention disclosed is described using specificimplementations as examples, it is intended only to be examples andnon-limiting. The practitioners of the art will be able to understandand modify the same based on new innovations and concepts, as they aremade and become available. The invention is intended to encompass thesemodifications that conform to the inventive ideas discussed.

What is claimed is:
 1. A method of operating an impedance injectionmodule (IIM) comprising a plurality of flexible alternating currenttransmission system (FACTS) based impedance injection units (IIUs), themethod comprising: controlling, by a control module of the IIM, theplurality of FACTS based IIUs of the IIM forming multiple connectionconfigurations in sequence, each connection configuration comprisingmultiple FACTS based IIUs in series, parallel or combination thereof,wherein the IIM is coupled to a transmission line; generating, by theplurality of FACTS based IIUs through the multiple connectionconfigurations, a plurality of synchronized rectangular impedanceinjection waveforms that, when injected into the transmission line, arecombined to produce a pseudo-sinusoidal impedance waveform; injectingthe generated synchronized rectangular impedance injection waveformsinto the transmission line and controlling power flow in thetransmission line using the pseudo-sinusoidal impedance waveform; andgenerating and injecting into the transmission line one or more shortduration pulses by at least one FACTS based IIU that is not beingutilized during that period of generating the synchronized rectangularimpedance injection waveforms.
 2. The method of claim 1, furthercomprising: sensing, by a plurality of sensors coupled to thetransmission line, presence of a disturbance on the transmission line;and combining the one or more short duration pulses with the pluralityof synchronized rectangular impedance injection waveforms to modify theproduced pseudo-sinusoidal impedance waveform to rectify the senseddisturbance.
 3. The method of claim 1, wherein the pseudo-sinusoidalimpedance waveform reduces generation of oscillations on thetransmission line, as compared to injection of a single rectangularimpedance injection waveform into the transmission line.
 4. The methodof claim 1, wherein the plurality of synchronized rectangular impedanceinjection waveforms are synchronized to generate a sequence ofrectangular waveforms that when combined and injected into thetransmission line, produces the pseudo-sinusoidal impedance waveform. 5.The method of claim 1, further comprising: synchronizing, through acommunication unit, the controlling of the plurality of FACTS based IIUsof the TIM and the generating of the plurality of synchronizedrectangular impedance injection waveforms with one or more clocks thatare local to the control module and the plurality of FACTS based IIUs.6. The method of claim 1, further comprising: synchronizing one or moreclocks that are local to the control module and the plurality of FACTSbased IIUs, to a Global Positioning System (GPS) clock.
 7. The method ofclaim 1, further comprising: generating one or more additional pulses ofshorter duration than the sequence, wherein when the one or moreadditional pulses are combined with the synchronized rectangularimpedance injection waveforms and injected into the transmission line,by the control module through one or more of the plurality of FACTSbased IIUs not otherwise being used during that period that produces thepseudo-sinusoidal impedance waveform, the pseudo-sinusoidal waveform ismodified in response to the sensed presence of the disturbance.
 8. Themethod of claim 1, further comprising: generating and injecting one ormore additional pulses to the transmission line, by the control modulethrough the plurality of FACTS based IIUs during their unused periods,to respond to and correct the disturbance on the transmission line. 9.An impedance injection system comprising one or more impedance injectionmodules (IIMs), the impedance injection system comprising: a pluralityof flexible alternating current transmission system (FACTS) basedimpedance injection units (IIUs) of an IIM; and a control module to:direct the plurality of FACTS based IIUs of the IIM to form connectionconfigurations in sequence, with each connection configurationcomprising multiple FACTS based IIUs connected in series, parallel orcombination thereof, wherein the IIM is coupled to a transmission line;generate, through the connection configurations of the plurality ofFACTS based IIUs in the sequence, synchronized rectangular impedanceinjection waveforms to combine and inject into the transmission line, toproduce a pseudo-sinusoidal impedance waveform on the transmission line,to control power flow in the transmission line; and generate, throughthe connection configurations of one or more of the plurality of FACTSbased IIUs, during an unused period in the sequence, one or more shortduration pulses to be combined with the synchronized rectangularimpedance injection waveforms and injected into the transmission line tocorrect a sensed disturbance on the transmission line.
 10. The impedanceinjection system of claim 9, wherein the control module further tosmooth the synchronized rectangular impedance injection waveforms toproduce the pseudo-sinusoidal impedance waveform to reduce generation ofoscillations on the transmission line in comparison to injection of asingle rectangular impedance injection waveform into the transmissionline.
 11. The impedance injection system of claim 9, further comprisingthe control module to synchronize the rectangular impedance injectionwaveforms to the sequence of connection configurations of the FACTSbased IIUs.
 12. The impedance injection system of claim 9, furthercomprising: a communication unit configured to synchronize theconnection configurations and the rectangular impedance injectionwaveforms with one or more clocks that are local to the control moduleand the plurality of FACTS based IIUs.
 13. The impedance injectionsystem of claim 9, further comprising: a communication unit configuredto synchronize one or more clocks that are local to the control moduleand the plurality of FACTS based IIUs, to a Global Positioning System(GPS) clock.
 14. The impedance injection system of claim 9, furthercomprising: one or more sensors, for connection to the transmissionline; and the control module to generate and inject, through one or moreFACTS based IIUs that are not at that time being used in the connectionconfigurations in the sequence, one or more additional pulses of shorterduration than the sequence, into the transmission line, the injected oneor more additional pulses to modify the pseudo-sinusoidal impedancewaveform in response to sensing a disturbance by the one or more sensorson the transmission line, wherein the modification of thepseudo-sinusoidal impedance waveform is configured as a correction forthe sensed disturbance.
 15. The impedance injection system of claim 9,further comprising: the control module configured to generate andinject, through the plurality of FACTS based IIUs, one or moreadditional short pulses into the transmission line, to respond to andcorrect a disturbance on the transmission line.
 16. A non-transitory,computer-readable media having instructions therein, which when executedby a processor, cause the processor to: direct a plurality of flexiblealternating current transmission system (FACTS) based impedanceinjection units (IIUs) of an impedance injection module (IIM) to formconnection configurations in sequence, with each connectionconfiguration comprising multiple IIUs connected in series, parallel orcombination thereof, wherein the IIM is coupled to a transmission line;generate, through the connection configurations of FACTS based IIUs inthe sequence, synchronized rectangular impedance injection waveforms tocombine and inject into the transmission line, to produce apseudo-sinusoidal impedance waveform on the transmission line to controlpower flow in the transmission line; and generate, through theconnection configurations of FACTS based IIUs, during an unused periodin the sequence, one or more short duration pulses to be injected intothe transmission line to correct a sensed disturbance on thetransmission line.
 17. The non-transitory, computer-readable media ofclaim 16, wherein the instructions, which when executed by theprocessor, further cause the processor to: synchronize the rectangularimpedance injection waveforms to the sequence of connectionconfigurations of FACTS based IIUs.
 18. The non-transitory,computer-readable media of claim 16, wherein the instructions, whichwhen executed by the processor, further cause the processor to:synchronize the connection configurations and the rectangular impedanceinjection waveforms with one or more clocks that are local to a controlmodule and the plurality of FACTS based IIUs.
 19. The non-transitory,computer-readable media of claim 16, wherein the instructions, whichwhen executed by the processor, further cause the processor to:synchronize one or more clocks that are local to a control module andthe plurality of FACTS based IIUs, to a Global Positioning System (GPS)clock.
 20. The non-transitory, computer-readable media of claim 16,wherein the instructions, which when executed by the processor, furthercause the processor to: sense a disturbance on the transmission linethrough one or more sensors; and generate and inject, through one ormore FACTS based IIUs that are not at that moment being used in theconnection configurations in the sequence, one or more additional pulsesof shorter duration than the sequence, into the transmission line, tomodify the pseudo-sinusoidal impedance waveform, in response to sensingthe disturbance on the transmission line.
 21. The non-transitory,computer-readable media of claim 16, wherein the instructions, whichwhen executed by the processor, further cause the processor to: generateand inject, through the plurality of FACTS based IIUs, one or moreadditional short duration pulses to the transmission line, to respond toand correct a disturbance on the transmission line.